Mainframe computer systems, such as the IBM 3990, the IBM 4381, and the UNISYS 2200/200, send and retrieve data to and from storage facilities via storage controllers. Such mainframe computers communicate with their peripheral storage facilities, such as disk and tape systems, via one or more "channels." These channels carry commands and data between the computer and the storage facilities. The channels extend between, or "bridge" the gap between, the mainframe computer's main processor (i.e., the CPU) and the storage controller. The storage controller then interprets the commands and manipulates the storage facilities to satisfy a request.
Mini computers also communicate with storage facilities via storage controllers. Normally, storage controllers for mini computers are far less sophisticated than those for mainframe computers; however, they provide essentially the same, albeit more limited, services or functions. For example, in mini computer systems, storage controllers are typically held on a common bus, rather than on separate channels for each string of disks or other storage devices. The bus provides similar functions to that of the channel, except that only one controller on a particular bus can be active at one time. In channel architecture, which is provided on mainframe computers, all the channels may be active simultaneously. Thus, mainframe computers have much wider maximum I/O band widths than mini computers.
At the present time, due to rapid advances in peripheral technologies, newly developed storage facilities are available which have increased capabilities in areas such as efficiency and size. For example, rewritable optical disks, optical tapes, and 4 mm digital tapes (DAT) are each known for their large storage capacities, reasonably quick access time, and low floor space and power requirements. However, in order for current mainframe and mini computers to access these improved storage facilities, specialized storage controllers must be developed (or purchased) which may handle such storage facilities. For example, in order to facilitate connection of mainframe FIPS 60 channels to a SCSI storage device interface, several specialty manufacturers provide plug-in boards which allow VME base computers, such as the SUN, to intercept FIPS 60 channel inputs. However, these products have been provided by small organizations for limited specialty applications; they are not generic storage controllers which will support all or a significant portion of newly developed storage facilities.
Another significant limitation of conventional storage controllers is that they are typically limited in their ability to communicate with only the specific operating system of one host computer system. Although many mainframe channels utilize the FIPS 60 channel communication protocol, for each unique operating system (e.g., UNIX, OS/2 DOS, AIX), the channel program command set will have a unique "dialect." Thus, "host-specific" storage controllers must be provided to support each operating system.
There is a tremendous cost associated with buying or developing specialized (host specific and/or storage device specific) storage controllers. Thus, there is a need for a generalized, versatile, programmable storage controlling system which would allow various host computer systems to utilize, and thus benefit from, the increased advantages of new peripheral storage facilities that are now available, or which will be available in the near future.